[john marcella]

From over on YB. For some of you here it may be easier to take from George than it was from me the last go around. (NHRA Pro stock bike engien builder)
^^^not intended to start crap or bash, just a little friendly smartassizum

http://www.yellowbullet.com/forum/sh...d.php?t=531428





--------------------------------------------------------------------------------

Many racers and fans still dont understand vacuum pumps and why they help.
I had to write a tech article once about this...
I am going to share it here, to open a once and for all thread on the hows and whys of the dreaded Vacuum pump....these are ideas and experience of mine and I welcome comments, questions and additional info to add .

Run up to a full 10th quicker with vacuum pumps!

Vacuum pumps can help you run up to a full tenth quicker.
They make lots of power increases because they allow the top ring to stay sealed "longer" in the rev range.
Many racers think it is because of other reasons, but, truth is, all pistons and rings will lose their seal at "some" rpm.
This is when the pressure below the ring is greater than the pressure above the ring.
When you rev the engine so high that the piston stops at TDC, the ring tries to keep going, losing contact with the bottom of the top ring groove.

So, the vac pump can pull negative pressure on the entire area under the rings.
It includes the sump area and all space under the pistons. The bigger the area, the more "storage" tank you have for vacuum.
What we have found over the years is that the oil system loses PSI at the same rate as the vacuum increases.
Vacuum is measured in inches of pressure and the oil system is measured in pounds per square inch.
So, the vacuum pump will reduce the oil PSI a little. Remember your gauge is zeroed to atmosphere, not inside the sump.

When we use the big electric vacuum pumps, we fire engine first, then turn on the pump. If you are racing, it will be up to full vacuum by the time you stage and you will have oil PSI.
The biggest danger when using the vac pump is starting the engine after an oil and filter change, because the entire oil PSI system is empty of oil and full of air.
If you turn on your vacuum pump before the oil PSI is primed back to normal, it is possible to run the engine dry of lube and you will lose the crankshaft.

If your vacuum pump pumps oil out into your overflow tank (puke tank), you have a bad leak in the system.
This could be anything from a minor manifold end seal or gasket leak, up to, as bad as a hole in a piston.
We run new and sealed gaskets and turn seals around backwards to maximize our vacuum advantages.
The more vacuum we pull on the crankcase, the higher we can rev the engine before ring seal loss.
Please be mindful of this information and write me for answers to questions.

Have fun and go quick!
__________________
The Power of the Bullet is AWESOME

"May the POWER be with you"


PROUD SPONSORS OF THE YELLOWBULLET .COM NATIONALS!!!!

We build only cool stuff, from HEMI to Harley
Please go to www.starracing.com and check us out.
We race cars and bikes.
Please go see www.b2cars.com to see HEMIs
My "day job" is hoppin up Harleys.

[slowbird]

Darn good read & great info!!!

[johnta1]

So, does this subscribe to your theory on vacuum pumps?

[cosgrove]

This shows a lack of understanding about how a closed system will be affected by pressure and vacuum. Starting an engine with vacuum in the crankcase will have NO effect on the oil system's ability to prime since it is pumping into an area that is also under vacuum.
An engine with no air in the crankcase (total vacuum) will show less pressure on the oil gauge, but that will have NO effect on the pressure or volume of oil that the bearings and other engine components receive. It shows less pressure on the gauge because it lacks the 14 psi atmospheric boost. But again it doesn't have to overcome this boost in the area the oil is being pumped into.
Here is a little thought experiment. Imagine a crankcase you could pressurize to 100 psi. The oil pressure gauge would now read 100 psi. (yes it will put pressure on the oil gauge). However oil will not magically start flowing through the oil system since it is a closed system. Now start this engine. If it normally produced 75 psi oil pressure, the gauge would now read 175 psi. (pump pressure plus pre-charge pressure). The pressure from the pre-charge has no effect on the oil system pressure or flow whether the engine is running or not.
Same with NO air in the crankcase of this imaginary engine(total vacuum). If you used a pressure/vacuum gauge on the oil system, it would read the equivalent of -14 psi (yes it would put suction on the oil gauge). However oil will not magically start flowing backwards through the oil system since it is a closed system. Now start this engine. If it normally produced 75 psi oil pressure, the gauge would now read 61 psi.(pump pressure minus the 14 psi atmospheric boost). The vacuum in the crankcase has No effect on the oil system pressure or flow whether the engine is running or not.
Oil pressure gauges on earth are calibrated to read 0 in our atmosphere. An oil pressure gauge will read a little less in an engine with a vacuum pump, not because it has less oil pressure but because the gauge is not calibrated right. It is calibrated for atmospheric pressure, not crankcase pressure.

[Tom Vaught]

[QUOTE=john marcella;4800176]From over on YB. For some of you here it may be easier to take from George than it was from me the last go around. (NHRA Pro stock bike engien builder)

Originally Posted by john marcella

From over on YB. For some of you here it may be easier to take from George than it was from me the last go around. (NHRA Pro stock bike engien builder)

"When you rev the engine so high that the piston stops at TDC, the ring tries to keep going, losing contact with the bottom of the top ring groove."

I believe John that every Piston has a dwell time in an engine, does it not?

Why would you have to "rev the engine so high that the piston stops" when the actual engine has a Dwell time at BDC and TDC for every revolution that it makes.

The guy might be a "NHRA Pro stock bike engien builder" but he is off a bit in his understanding of basic engine design principals. That being said, I have known many many smart racers who did not understand how the Physics worked but were outstanding tuners and engine builders (not engine designers).

Not starting ant **it either.

Agree or disagree, Does the engine Dwell at BDC and TDC no matter what the rpm is?

Tom Vaught

ps Agree, cosgrove, "george" doesn't understand several things.

[hill461]

can anyone tell me how to stop my vacum pump from pulling oil out . it will probably pull a quart out about every 10 passes. i have changed vacum regulators i have changed locations where i pull out of valve covers, currently running valve covers Butlers built for me. i have no oil leaks when removed and am running evac tubes. pulls 13-15 onces of vacum. pump came as a kit from tin indian.
any help would be appreciated
hill461

[cosgrove]

Originally Posted by hill461

can anyone tell me how to stop my vacum pump from pulling oil out . it will probably pull a quart out about every 10 passes. i have changed vacum regulators i have changed locations where i pull out of valve covers, currently running valve covers Butlers built for me. i have no oil leaks when removed and am running evac tubes. pulls 13-15 onces of vacum. pump came as a kit from tin indian.
any help would be appreciated
hill461

If your crankcase is tight(lets no air in), and your ring seal is very good, oil is easy to control. Otherwise it can be pretty tough. But where you pull air out of the motor is important. Pull from center of valve cover near the intake seems to work. A baffle there helps too.
Mine pulled more oil than that before new pistons and rings. Now it pull nothing but a little water vapor. Try running 12-13 hg.

[65 GTO Convert]

Originally Posted by cosgrove

This shows a lack of understanding about how a closed system will be affected by pressure and vacuum. Starting an engine with vacuum in the crankcase will have NO effect on the oil system's ability to prime since it is pumping into an area that is also under vacuum.
An engine with no air in the crankcase (total vacuum) will show less pressure on the oil gauge, but that will have NO effect on the pressure or volume of oil that the bearings and other engine components receive. It shows less pressure on the gauge because it lacks the 14 psi atmospheric boost. But again it doesn't have to overcome this boost in the area the oil is being pumped into.
Here is a little thought experiment. Imagine a crankcase you could pressurize to 100 psi. The oil pressure gauge would now read 100 psi. (yes it will put pressure on the oil gauge). However oil will not magically start flowing through the oil system since it is a closed system. Now start this engine. If it normally produced 75 psi oil pressure, the gauge would now read 175 psi. (pump pressure plus pre-charge pressure). The pressure from the pre-charge has no effect on the oil system pressure or flow whether the engine is running or not.
Same with NO air in the crankcase of this imaginary engine(total vacuum). If you used a pressure/vacuum gauge on the oil system, it would read the equivalent of -14 psi (yes it would put suction on the oil gauge). However oil will not magically start flowing backwards through the oil system since it is a closed system. Now start this engine. If it normally produced 75 psi oil pressure, the gauge would now read 61 psi.(pump pressure minus the 14 psi atmospheric boost). The vacuum in the crankcase has No effect on the oil system pressure or flow whether the engine is running or not.
Oil pressure gauges on earth are calibrated to read 0 in our atmosphere. An oil pressure gauge will read a little less in an engine with a vacuum pump, not because it has less oil pressure but because the gauge is not calibrated right. It is calibrated for atmospheric pressure, not crankcase pressure.

Post #7 in that thread

Originally Posted by George Bryce

We pull 25 inches on wet sump and 25 inches on dry sump...the oil psi reduction is in gauge reading only.
If you put put the gauge inside the oil pan, it would still be the same as with out vacuum pump.
Please have other engine builders chime in.

[mike leech]

These are the most over thought threads on this board. MAJOR EYE ROLL and FACE PALM.

[cosgrove]

Originally Posted by mike leech

These are the most over thought threads on this board. MAJOR EYE ROLL and FACE PALM.

It's because we're such "deep thinkers". LMAO

[mike leech]

Yes LMAO!

[wrench]

Agree or disagree, Does the engine Dwell at BDC and TDC no matter what the rpm is?

Tom Vaught



Anything that reverses direction traveling on a straight line has to "stop" at one point. I read his point to be, that at high RPM the ring wants to keep traveling when the piston is stopped? I don't have any idea how that relates to anything, but I think that was what he was saying?

[mike leech]

Originally Posted by wrench

Agree or disagree, Does the engine Dwell at BDC and TDC no matter what the rpm is?

Tom Vaught



Anything that reverses direction traveling on a straight line has to "stop" at one point. I read his point to be, that at high RPM the ring wants to keep traveling when the piston is stopped? I don't have any idea how that relates to anything, but I think that was what he was saying?

bingo

[Half-Inch Stud]

Originally Posted by mike leech

These are the most over thought threads on this board. MAJOR EYE ROLL and FACE PALM.

We use a vacuum pump on a rotary engine, with a dry sump. It works well.

[Half-Inch Stud]

Could be for Rotor cooling too, depending on how ya look at these things.